A trade-off study between diversity branches and channel estimation errors in broadband wireless communications

To adapt to the adverse radio environment efficiently, we investigate the use of two code division multiple access (CDMA) based broadband systems. In one of these systems, information symbols are transmitted simultaneously and in other system, information symbols are chip-interleaved before transmission. We analyze that both of these systems exploit temporal variations in the channels so efficiently that using the estimated channel coefficients they are capable of outperforming the conventional system with perfect channel state information (CSI) at the receiver. However, due to channel estimation errors, unlike the conventional system with perfect CSI, both systems with estimated CSI are not always benefitted by additional multipath or temporal diversities. At high signal-to-noise ratio (SNR), there is an optimum diversity order in those systems with estimated CSI.; We show that the chip-interleaved system is somewhat more efficient in terms of allocating energies between information and pilot symbols than the system that transmits information symbols simultaneously. Both systems exhibit almost identical performance when the system load is high. However, when the system load is light, the chip-interleaved system slightly outperforms its counterpart due to higher self-interference in the latter. Their performance difference is less with estimated CSI than with perfect CSI.